Manufacture of submarine or other signaling cables



Feb. 6, 1934.* w. s. SMITH ET AL 1,945,337

MANUFACTURE OF SUBMARINE OR OTHER SIGNALING CABLES Filed dan. 2, 1931 5) Th'f/IP A TT'ORNEYS,

Patented Feb. 6, 1934 MANUFACTURE 0F SUBMARINE GR OTHER SIGNALING @ARLES Willoughby Statham Smith, lBenchams, Newton Poppleford, Henry Joseph Garnett, hymne,

Soleiields, Sevenoaks, a

`rpington, England nd .lohn Norman Deana Application January 2, 3193i, Serial No. 505,306, and in Great Brit January 8, lg3d 5 illai.

This invention relates to the manufacture ci submarine or other signaling cables insulated 'with gutta perche., balata and the like or their substitutes, and more particularly such cables which incorporate a preparation derived from coal tar for preservative or other purposes.

llt is common practice in the manufacture of e. g. submarine cables, to treat the outer servings ci jute or hemp with coal tarte preserve them. it is also well known that it is necessary to tree the .tar used ior this purpose from. its more volatile constituents, as the latter have a harin-1 iul elect upon the gutta percha insulation, ren dering it in the course of time sticky.

llt has new been iound that the acid and basic constituents remaining in the tar ai'ter the incre volatile constituents have been removed have a harmful effect upon the electrical properties oi the gutta perche. or the like.

according to the present invention submarine or other signaling cables in which there is in= sulation ci gutta percha, balata, rubbenor other 'like 'thermoplastic materials or mixtures there-a of or preparations therefrom with or Without additional. ingredients and in which a composi tion being or comprising a preparation derived from coal tar is used, e. g. lor coating or iinpregnating the servings ci the cable, so that the insulation is subjected to its irnluence, are inane uiactured using as such composition one vvhose coal 'tar constituents are substantially :tree irorn acid and basic components as well as from the incre volatile components of coal tar whereby the hariniul eect on the insulation is prevented or reduced.

The acid is or" a phenolic nature and the tar bases are amino-bodies of the aromatic series as will appear from a consideration ci the temperatures hereinafter given.

@ne way of removing these undesirable acid and basic constituents from the tar is to subject the tar steam. distillation. This treatment,

however, removes not only these undesirable con-I stituents but also at the same time useful oils of a harmless nature, with the result that after treatment with steam, the tar has thickened until in some cases it sets to a hard and brittle solid at sea-'bottom temperatures. Such tar is, of course, useless for impregnating the jute or hemp servings, as it would tend to make the cable inflexible. .a iurther disadvantage is that it is extremely dimcult to remove the basic substances from the tar completely by this method.

Another way of removing the acidic and basic constituents is by treating the tar rst with an alkali to combine with the acidic bodies, Washing thoroughly with Water to remove the salts thus formed, together with any excess oi alkali, and then treating the tar with acid to combine with the basic bodies and :ilnally washing again c() with Water to removethe salts and excess oi acid.

The disadvantages ci this methodY are that the nist place it is very diicult to Wash the tar thoroughly with water as, especially in the pres c5 ence of alkali, there is a tendency tor the moix= ture to form an emulsion, and inthe second place when sulphuric acid is used in the removal oi the basic substances, it .is very liable to sulphonate the tar yielding products that are highly lo undesirable ior the purposes of protection.

Tar for use in accordance `with this invention may be prepared by Asubjecting the tar to a distillation at a temperature suiilcient .to distli oil the usei'ul oils, which oil containing portion i5 oi the distillate is collected and subjected to a separate treatment to remove the acidic and basic impurities, when the purified oil is returned to the original body oi tar which is then ready flor use. d@

in the preferred method, the purined tar is obtained by iirst removing the more volatile constituents by distillation in the usual Way, then continuing the distillation until the harmful acidic and basic substances have been yremoved. The oily part of the distillate, which, in. order to maintain the naphthalene content as low as possible, should not be collected below 225-230` C., is now treated lirst with an alkali o and then with an acid with intermediate and final washings, as described above, and is iinally returned to the body of the pitch. lt will be found that distillation can conveniently be stopped at about 3D0-315 C.. 95

It has been round that another very suitable r preparation consists substantially of anthracene oil and pitch. in which the anthracene oil is rst washed with acid and alkali to remove tar bases andacids. The anthracene oil is obtained by collecting the distillate between about 27 5315 C., or according to usual practice.

The ratio of the contents of anthracene oil to pitch will vary according to the quality of the tar from which the constituents have been obtained, and the temperature to which the still was taken before discontinuing the distillation of the oil.

Suitable proportions are from about to 30% of anthracene oil, and the remainder pitch.

The viscosity of the resulting tar will vary according to the requirements, and these will in turn depend, for example, upon the temperature to which the cable is to be submitted.

A tar with the following analysis has been found very suitable.

`Specific gravity 1. 2 Viscosity -25 secs. (Hutchinson) 'I'he methods used for the analysis are according to Standard Methods for Testing Tar and its Products', published by the Standardization of Tar Products Tests Committee, December, 1929.

Tars so treated are suitable for general use in the protective coatings or cable compounds of submarine signaling cables or of any cables where gutta percha, balata or the like or their substitutes, e. g. rubber or purified rubber and their mixtures with Wax and/ or any thermoplastic material suitable for insulation purposes, is used. For example the jute may be impregnated with the treated tar or with compositions in which the tar proportion consists of the treated tar.

It was formerly believed that the preservative action of tar was due to the presence therein of phenolic bodies. Recent tests have proved, however, that tar from which all water-so1uble bodies, including the phenols, have been removed has its preservative action enhanced, probably owing to the fact that its water-absorbing power is thereby greatly diminished. Tar refined by the improved method described above will therefore show enhanced protective properties towards the jute, and has no harmful action on the gutta percha.

Examples Method of testing.-Samples of the tar before and after treatment were placed in separate vessels and a measured length of core having a gutta percha insulation was suspended over the tar in each vessel. A similar core placed in another vessel containing no tar was used as a control. The vessels were now sealed and allowed to remain for a number of days.v The dielectric resistance of each piece of core was measured before and after suspension over the tar.

Exnux.: 1

Steam-blown Tar Before suspension over the tar, all the samples had substantially identical dielectric resistances ln water at '15 F. After being suspended over Untreated Treated Nc tar' tar tar 8% riso 10% drop 5% riso EXAMPLI fi' Acid and base-freed tar Before suspension over the tar, all the samples, had substantially identical dielectric resistances in water at '15 F. After being suspended over the tar for days, the following changes were found to have occurred in the dielectric resistance in water at F. of the gutta percha:-

Untreatod No tar tm.

Treated tar 10% rise 12% drop 9.5% rise In some cases it may be desirable to renne the tar still further by removing the so-called free carbon. This may be done by any known method, for example by nltration hot through cloth or metal cloth with or without the use of a filter aid.

The invention is illustrated in the accompanying drawing which shows a cross section of a submarine cable constructed in accordance with the invention.

In the drawing, 1 indicates the core comprising a central conductor and loading next to which is a layer indicated at 2 of Chattertons compound. Surrounding the layer 2 are three layers 3, 3' and 3 of gutta percha insulation over which insulation is wound a brass teredo tape 4. On the outside of the teredo tape 4 is a layer of tarred jute 5 surrounding which are armor wires 6. The remainng layers consist of an inner layer of compound 7, a layer of tarred jute 8, an intermediate layer of compound 9, another layer oi.' tarred jute 10, and finally an outer or closing layer 11 o1' compound.

The special tar can be used to advantage in layers 7, 8, 9, 10 and 11. It may be stiiened, if necessary, with such substances as pitch in order to obtain compounds of suitable stiffness and rigidity.

1. In a signaling cable, conducting meansl a thermoplastic insulation for said conducting means embodying gutta percha or the equivalent,

and a coal tar containing body in said cable in proximity to said gutta percha insulation so that the latter is subjected to its'inuence, the coal tar being substantially free from acid and basic components as well as the more volatile components. i

2. In a signaling cable, conducting means, a thermoplastic insulation prepared from gutta percha, and servings treated with coal tar in said cable in proximity to said insulation so that the latter is subjected to the influence of the coal tar. the coal tar being substantially free from acid and basic components as well as the more volatile components.

3. In a signaling cable, conducting means, a thermoplastic insulation prepared from gutta 5. A signaling cable as claimed in claim 1 in which the tar is substantially a mixture of 10 to 30% anthracene oil substantially free from acid' and basic components as well as the more volatile components, and pitch.

WILLOUGHBY STATHAM SLUTH. HENRY JOSEPH GARNETT. JOHN NORMAN DEAN. 

